What is the average atomic mass of element X: X- 10 98%
X - 11 1.5%
X - 12 0.5%
The answers to pick from are 10.025 amu or 11 amu or 10,565 amu or 12.05 amu.

The average atomic mass of element X is 10.025 amu

The average atomic mass of element X = atomic mass of 10 isotope × relative abundance of 10 isotope + atomic mass of 11 isotope × relative abundance of 11 isotope + atomic mass of 12 isotope × relative abundance of 12 isotope

= 10 × 98% + 11 × 1.5 % + 12 × 0.5 %

= 10 × 0.98 + 11 × 0.015 + 12 × 0.005

= 9.8 + 0.165 + 0.06

= 10.025 amu

So, the average atomic mass of element X is 10.025 amu

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